District Attorney Daniel Donovan speaks during a press conference last year. Today, prosecutors upped the charges against Jose Sandoval to second-degree vehicular manslaughter.STATEN ISLAND, N.Y. -- The 24-year-old driver accused of killing his school teacher girlfriend in a drunken wreck on the Staten Island Expressway Sunday repeatedly fretted over how the woman’s mother would react, authorities allege.

“What did I do? How am I going to explain this to her mother?” Jose Sandoval of South Park Slope, Brooklyn, told investigators after the crash, according to a law enforcement source.

His girlfriend, Lucia Negrete -- who was 25 and a math teacher at Franklin K. Lane High School in Cypress Hills, Brooklyn -- died on the scene at about 2:30 a.m., after his 2002 Honda crashed into a guardrail on the Brooklyn-bound side of the Expressway.

Today, prosecutors upped the charges against Sandoval to second-degree vehicular manslaughter, a felony punishable by two and a third to seven years in prison if he’s convicted at trial, said William J. Smith, a spokesman for District Attorney Daniel Donovan. He’s also charged with criminally negligent homicide and operating a motor vehicle while intoxicated.

Sandoval, who authorities said was admitted to Staten Island University Hospital, Ocean Breeze, with a head injury, was not arraigned in Stapleton Criminal Court today. That court appearance is expected to take place tomorrow.

As police and law enforcement sources tell it Sandoval lost control of his car near the Expressway’s Richmond Avenue exit. He hit a guardrail head-on, then started spinning, and hit the highway’s median.

Ms. Negrete, who was in the passenger’s seat, was launched through the rear windshield.

“It was a combination of speed, alcohol and the wet pavement,” said one police source.

Sandoval took a breath test on the scene that revealed his blood alcohol level was .239 percent — nearly three times the .08 percent legal threshold — according to authorities.

When asked if he’d consent to a blood test, though, he refused and responded, “I plead the fifth,” a law enforcement source said.

Sandoval told police he had thought another car hit him, though no other car appeared to be involved in the wreck, the source said.